In previous mechanical pencils, breakage of the lead-carrying mechanism has occasionally occurred when the mechanism was briskly retracted against the upper or lower ends of the guide tube. The damage usually consists of deformation of the radially extending ears of the mechanism.
It is an object of this invention to provide a clutch unit between the lower end of the worm spring which drives the lead-carrying mechanism, and the upper end of the bushing which is fixed to the upper exterior cap. The clutch unit permits relative slippage between the bushing and the worm spring when the relative torque therebetween exceeds a selected level.